Coatings are used extensively by the graphic arts printing industry to protect and enhance products. The graphic arts printing industry and its packaging segment commonly apply coatings and other finishes to aesthetically and protectively improve printed materials and substrates, including business cards, catalogues, brochures, posters, publication covers, folding cartons, blister cards, shrink wrap films, and labels. Merchandisers are seeking a product that appeals to the consumer with a unique design and graphic appearance that differentiates their product from the rest.
Holographic, microstructure or refractive images, and other surface finishing techniques, are widely used in a variety of decorative and security applications, including throughout the graphic arts and converted industries to create flexible substrates and materials with a unique and distinctive look. Holographic and other microstructure or refractive images are applied to printed material to capture the visual attention of the viewer by producing elaborate visual effects via light refraction and reflection. Such applied imagery can produce different viewing effects depending on the viewing angle, light source, and image details. Additionally, holograms and other microstructure imagery are often used to authenticate the genuineness of a product and increase the difficulty of counterfeiting.
Due to the mechanical application techniques involved, all graphic arts coatings and finishes, including mirror, textured, and holographic finishes, are apt to vary in the quality of the finished product. Oftentimes, in order to perform such coatings and finishes, a printed substrate must be removed from the printing press where the ink was applied and placed in separate machines that perform the duties of coating, ultraviolet curing, and the like. This results in a variation in appearance and an inconsistent look being presented to the purchasing consumer, who is attracted to the sales appeal of an aesthetically appealing finished printed product.
The predominant method of applying holograms to flexible substrates has been the lamination of an embossed holographic film such as PET (polyethylene terephthalate) or BOPP (biaxially oriented polypropylene) to the substrate. This method provided a decorative effect and served as a deterrent to counterfeiting; however, it consumed additional raw materials, it prevented the recycling of paper and paperboard substrates, and it increased manufacturing costs.
An alternative method for applying holographic and other microstructure images used heating, as disclosed in U.S. Pat. No. 5,155,604, and while eliminating the need for lamination, it created other important drawbacks. For example, applying holograms to rigid resin substrates with a heated cylinder to form microstructure images in a hardened resin substrate can produce image distortion because of the substantial heat and pressure required to impress the image into the rigid substrate. Similarly, applying further heating to previously heat-impressed films, such as the heat necessary to apply shrink film webs with microstructure images to container surfaces, can distort the images, effectively causing them to disappear or to lose some of their holographic or other refractive properties. Moreover, many graphic arts, converting, and packaging substrates are heat sensitive, and exposure to temperatures at or above 30° C. would damage or destroy the substrate.
A method employed in the prior art for casting holograms or other images in registration with printing on a substrate uses a holographic or other image embedded in a cylinder or film; consequently, it can transfer shim lines or other unwanted patterns to the finished product. For example, electroformed metal masters may be welded together or plastic masters may be ultrasonically butt-welded, or a number of masters may be adhered to the surface of the cylinder with the impressing surfaces of the masters facing out. In each case seams are present which can be impressed onto the receiving substrate along with the intended imagery.
Systems for impressing holographic and other microstructure or refractive images into a layer of curable liquid resin using cylinders with adjacent relief image masters (as described above) and then curing are also known. These systems suffer shortcomings in addition to those stemming from the seams between adjacent masters on the cylinder. For example, it is difficult to maintain accurate registration between the impressing image on the cylinder and printing on the substrate carrying the curable liquid resin. This problem is exacerbated when the system is run at high speed. Indeed, current systems for impressing holographic and other microstructure or refractive images into a layer of curable liquid resin using cylinders with adjacent relief image masters offer no means for fine tuning the alignment between the impressing image on the cylinder and printing on the substrate carrying the curable liquid resin.
As manufacturers have increased their use of holography and diffractive patterns to improve security, counterfeiters have responded by developing increasingly sophisticated counterfeiting methods. Counterfeiters may use an exposed cast surface image itself to create a duplicate master of a holographic, refractive, or diffractive effect.
Packaging professionals seek visual impact, functionality, recyclability and sustainability, and cost effectiveness. Visual impact drives shelf appeal; it improves market differentiation; and it improves packaging value added. Functionality is a requirement, for no matter how good a package or product looks, it must perform on the packaging line and on the shelf. Current environmental awareness increases the need for packages and products that are recyclable and sustainable. Last, a package or product must be affordable; consequently, the methods used to produce the package or product must be cost effective.
Accordingly, what is needed is an environmentally friendly, cost effective method or apparatus for creating holographic, microstructure, refractive and reflective images in registration on a substrate, which may eliminate repeat lines, reduce image distortion, and is compatible with temperature sensitive substrates. Further, there is a need for a method or apparatus that achieves accurate registration at high speed and accommodates large images.